Buckling Analysis Of In-service Tanks Based On Measured Settlement

With the advantage of low material consumption,small footprint,low cost and convenient maintenance,vertical steel tanks are widely employed in national strategic petroleum reserves.Settlement of foundation will have a great influence on the structure and mechanical properties of in-service tanks.It could cause buckling of tanks and endanger safety of petroleum reserves.Field measurement,theoretical derivation and nonlinear finite element numerical simulation methods are used to research buckling behavior of in-service tanks under settlement and combined settlement with axial load in this thesis.The main works are as follows:(1)Foundation settlements of G1307 and G106 in-service tanks in CNOOC of Ningbo are measured in site by the leveling method.Elevations of each measurement point constructed on these two tanks are obtained.Loop error of the measured result is analyzed to ensure accuracy of the measured settlements.(2)A settlement curve fitting method based on measured settlements is presented.For two different cases when the number of measurement points is odd and even,discrete Fourier transform is applied to derive the settlement theoretical expression in the form of Fourier series that distributed continuously in the circumferential direction beneath the tank wall.The full utilization of all measured settlement data is realized by this method and the actual settlement condition beneath the tank wall is accurately reflected.(3)A buckling stability analysis method for in-service tanks based on real time measured settlement by Riks nonlinear large deformation numerical simulation technique is presented.Buckling behavior of fixed-roof tank and floating-roof tank under differential settlement is simulated.Relation between tank wall deformation and differential settlement is analyzed.Effects of primary wind girder size on deformation and buckling of floating-roof tank are researched.Effects of liquid storage on the structural response of fixed-roof tank and floating-roof tank are researched then.(4)A buckling prediction method for in-service tanks is presented by applying least square principle and Lagrange quadratic interpolation based on measured settlements at different times.The Poisson curve prediction models corresponding to each measurement point are established and settlements beneath the tank wall at any moment in the future can be predicted then.Structural responses of in-service tank under settlements at different times are simulated and analyzed.The critical buckling time of in-service tank under settlement can be predicted.Difference of structural responses between fixed-roof tank and floating-roof tank under the same measured settlement is compared.(5)A buckling analysis method for in-service tanks under combined settlement and axial load is presented.Buckling behavior of in-service tanks with constant thickness and stepwise variable thickness under combined settlement and axial load is simulated and analyzed based on real time measured settlement by nonlinear large deformation numerical simulation technique.An arctan function is established to describe the stepwise variable thickness.By using the methods of separation of variables,small parameter perturbation and Fourier series expansion,analytical formulas of the critical buckling load for tanks with stepwise variable thickness under axial compression are derived.Effects of settlement on stability of in-service tank under axial load are analyzed.Buckling behavior of in-service tanks with different liquid heights under combined settlement and axial load is simulated and effect of liquid storage on the buckling behavior is analyzed.